No abstract

We have studied the l/f noise current in narrow gap semiconductor heterostructure diodes fabricated in mercury cadmium telluride (HgCdTe) and designed to operate in a non-equilibrium mode at room temperature. HgCdTe heterostructure diodes exhibit Auger suppression giving current-voltage characteristics with high peak-to-valley ratios (up to 35), and low extracted saturation current densities (e.g., 20 Acm -2 at 10 ~m at 295K) but high l/f knee frequencies (e.g., 100 MHz at 10 ~m at 295K). A comparison is made with the noise levels found in room temperature non-equilibrium mode heterostructure InA1Sb/InSb diodes. The devices are being used at high frequencies for CO~ laser heterodyne detector demonstrators. For the devices to be useful in low frame-rate imaging arrays, the 1/f noise level must be sufficiently low that the signal is not swamped. Ideally, the knee frequency should be below the frame rate. The relationship between the noise current and reverse bias voltage, current density, and temperature will be examined in order to attempt to identify the principal 1/f generation mechanisms.

No abstract

This paper reviews the current status of the growth of fully doped HgCdTe (MCT) devices by metalorganic vapor phase epitaxy (MOVPE). The current reactor system has been developed to produce 3-inch diameter epitaxial layers compatible with slice-scale processing. The new reactor system has achieved routine epitaxial growth of MCT with good morphology onto both gallium arsenide (GaAs) and GaAs on silicon (Si) wafers that were oriented (2-8°) off (100) orientation. The density of surface defects (so-called ''hillocks''), typical of MOVPE growth on such orientation substrates, has been reduced to ,5 cm ÿ 2 at a sufficient yield to make the production of low cluster defect 2D arrays possible. Alternative growth experiments onto cadmium telluride (CdTe) on Si substrates with (211)B orientation have also been performed to investigate their usefulness for infrared focal plane array (IRFPA) applications. Si substrates give better thermal expansion match to the read out Si circuits (ROIC). The horizontal reactor cell design has a graphite susceptor with a rotating platen capable of using substrates up to 4-inch diameter. Work, however, has concentrated on 3-inch diameter GaAs and GaAs on Si wafers substrates in the reactor, and these reproducibly demonstrated good compositional and thickness uniformity. Cut-off wavelength and thickness uniformity maps showed that there was sufficient uniformity to produce twelve sites of large format 2D arrays (640 3 512 diodes on 24-mm pitch) per slice. Minority carrier lifetimes in heterostructures is an important parameter and some factors affecting this are discussed, with special emphasis on As-doped material grown under various growth conditions in an attempt to reduce Shockley-Read (S-R) trap densities. New data are presented on trap densities and theoretical fitting of lifetimes in MOVPE material. Fully doped heterostructures have been grown to investigate the device performance in the 3-5 mm medium-wave IR (MWIR) band and 8-12 mm long-wave IR (LWIR). These layers have been fabricated into mesa arrays and then indium-bumped onto Si multiplexers. A summary of the 80-K device results shows that stateof-the-art device performance has been demonstrated in MOVPE-grown device structures.

We have investigated the negative luminescent properties of a HgCdTe device, fabricated from a 1 mm diameter array of photodiodes having peak emission at a wavelength of 8.5 μm. This long-wavelength luminescence is of sufficient efficiency and area to be useful in device applications.